Mammalian atrial tissue contains a peptide referred to as atrial natriuretic factor (ANF) that can be released under a variety of conditions into the general circulation. We have shown previously that atriopeptin III (APIII), a synthetic form of ANF, decreases cardiac output and lowers mean arterial pressure. Lack of reflex cardioacceleration to the APIII-induced reduction in blood pressure prompted an investigation into the effect of APIII on baroreceptor function in the intact conscious rat. Mean arterial pressure changes were elicited with bolus injections of phenylephrine (PE) and nitroprusside (NP). The dose of APIII employed did not change basal heart rate, mean arterial pressure (MAP) or the MAP response to PE or NP. The bradycardiac response to PE was accentuated and the baroreflex sensitivity increased by APIII. No significant effect on NP-induced changes in heart rate were observed. In the conscious rat, APIII selectively enhances the baroreflex response to increases, but not decreases, in arterial pressure.